Fix EventSource test to be aware of ArrayPoolEventSource

Commit migrated from https://github.com/dotnet/corefx/commit/e3218bc51da464a8c3033c2d75e78ae69e56de48

src/libraries/System.Diagnostics.Tracing/tests/BasicEventSourceTest/TestUtilities.cs

@@ -23,7 +23,8 @@ public static void CheckNoEventSourcesRunning(string message = "")
             foreach (var eventSource in EventSource.GetSources())
             {
                 if (eventSource.Name != "System.Threading.Tasks.TplEventSource"
-                   && eventSource.Name != "System.Diagnostics.Eventing.FrameworkEventSource")
+                   && eventSource.Name != "System.Diagnostics.Eventing.FrameworkEventSource"
+                   && eventSource.Name != "System.Buffers.ArrayPoolEventSource")
                 {
                     eventSourceNames += eventSource.Name + " ";
                 }